They can be bad, we had a bad one on the 89YJ, that small spring loaded cap broke off and the YJ ran like crap. They are about $89 or so. We put one in out of a junkyard XJ, same year and it ran worse. Finally had to put a new one it. Might want to check the filter under it, they sometimes get plugged with mud, $1.00 or so at AA.
The charcoal cannister is that big black coffee can sized thing with the 4 hoses running out of it.